1. Field of the Invention
The present invention relates to a metal head for a golf club, which is tough and has a relatively large volume without increasing the weight, and can be manufactured with ease.
2. Description of the Related Art
Metal wood heads and iron heads are generally produced by a precision casting process (lost wax process) using, as a material, a stainless steel such as SUS 630 [AISI (American Iron and Steel Institute) Standard Type 630]or SUS 431 (AISI Standard Type 431).
It is desirable for a golf-club head to make a golf club to which the head has been attached which is easy to swing and hard to cause a bad shot. Therefore, efforts have been made in reducing the weight of the head to make it easy to swing a golf-club to which the head has been attached, and widening the sweet spot in a face of the head or increasing the moment of inertia of the head to lessen the chance of a bad shot. With a wide sweet spot of the head, the course of flying of a hit ball becomes stable even if a hitting position in the face at which a ball is hit is irregular, and thus, the chance of a bad shot can be decreased.
On the other hand, a high moment of inertia of the head suppresses the turning of the head due to a shock upon hitting a golf ball, bringing a substantial widening of the sweet spot that stabilizes the course of flying of the hit ball.
In the case of a metal wood head of a hollow structure, for example, a portion near the sole of the head is made heavier than its crown to lower the center of gravity, whereby the sweet spot can be widened. It is also possible to increase the volume of the head, thereby to increase the moment of inertia of the head and widen the sweet spot.
In the case of an iron head on the other hand, a peripheral portion of the head, such as a toe or a heel, can be made heavier than a portion about the center of gravity of the head, thereby widening the sweet spot.
With an increased overall weight of a head, even if the sweet spot can be widened, it becomes difficult to swinging the golf-club to which the head has been attached. On the other hand, when the shell thickness of a head is thinned wholly or partly to suppress the weight, disadvantages of a reduced strength of the head and/or a lowered rebound of the ball upon hitting may arise. In the case of a head made of a conventional stainless steel, since the reduction of their thicknesses has reached the lower limit, widening of the sweet spot by the above-described methods is difficult to achieve.
There has been developed a golf-club head made of a titanium alloy. The titanium alloy has strength substantially equal to that of the stainless steel and a specific gravity lower than the stainless steel. The use of the metal lower in specific gravity permits the increase in the volume of the head and the peripheral portions of the head to be made heavier than other portions without increasing the overall weight of the head.
However, problems are pointed out that the titanium alloy is considerably expensive, and it requires a special vacuum melting casting machine for manufacturing a head by a precision casting process because of its high level of chemical activity.